Stabilization of acrylonitrile fibers to hot-wet creep

ABSTRACT

A process is provided for improving the dimensional stability under hot-wet conditions of fibers prepared from acrylonitrile polymers containing at least 95 percent acrylonitrile wherein spun fibers after orienting and drying are heated with wet steam under pressure to a temperature below the temperature where they shrink until the tendency to creep under hot-wet conditions is reduced.

United States Patent Charles Alexander Ball Mount Vernon, N.Y.

Jan. 8, 1971 Nov. 30, 1971 American Cyanamid Company Stamford, Conn.

Inventor Appl. No. Filed Patented Assignee STABILIZATION OFACRYLONITRILE FIBERS TO HOT-WET CREEP [56] References Cited UNITEDSTATES PATENTS 2,920,934 1/1960 Schaefer et al. 264/184 3,447,998 1/1969Fitzgerald et al. 264/210 Z 3,463,846 8/1969 Nakagawa et al 264/182FOREIGN PATENTS 43/22,358 9/1968 Japan 264/ l 82 44/7388 4/1969 Japan264/182 Primary Examiner-Jay H. Woo Attorney-Philip Mintz ABSTRACT: Aprocess is provided for improving the dimensional stability underhot-wet conditions of fibers prepared from acrylonitrile polymerscontaining at least 95 percent acrylonitrile wherein spun fibers afterorienting and drying are heated with wet steam under pressure to atemperature below the temperature where they shrink until the tendencyto creep under hot-wet conditions is reduced.

STABILIZATION OF ACRYLONITRILE FIBERS TO HOT- WET CREEP This inventionrelates generally to fibers prepared .rom

acrylonitrile polymers and, more particularly, to a method of 5improving the dimensional stability of such fibers under hotwetconditions.

Various processes for preparing fibers from acrylonitrile homopolymers,copolymers, terpolymers and the like have been proposed. Such processesinvolve dissolving the polymer in a suitable solvent therefor andspinning fibers therefrom by extruding the solution through aspinnerette into a coagulating bath. One such process is disclosed byCresswell in U.S. Pat. No. 2,588,730. In accordance with the Cresswellprocess, a water coagulable solution of the polymer is extruded into anaqueous coagulant maintained at a temperature of not more than about 1 0C.

One disadvantage of fibers prepared heretofore from acrylonitrilepolymers is lack of dimensional stability under hot-wet conditions.Fabrics prepared from such fibers tend to shrink or elongate when theyare dyed, washed or steam pressed. The tendency of fibers to shrink hasbeen more or less eliminated by preshrinking the fibers with steam underpressure after the fibers have been oriented by stretching. For example,the process disclosed in U.S. Pat. No. 2,920,934 not only reducesfibrillation but also reduces shrinkage of the resulting fiber. Inaccordance with that process, fibers prepared from polymers containingat least 70 percent acrylonitrile are subjected to wet steam in anautoclave under a pressure of 30 to 60 p.s.i.g. and a temperature wherefibers of such polymer composition shrink. As most apparent from table1, column 8 of the patent, the elongation of the annealed shrunkenfibers is greater than that of an unannealed fiber of the samecomposition.

Another process for improving the quality of filaments prepared frompolymers containing acrylonitrile by treating the filaments with steamis disclosed in U.S. Pat. No. 3,101,245. That process combines a dryingstep under controlled humidity with a subsequent steam treatment. Thefilaments are subjected while relaxed to steam at a temperature between105 C. and 160 C. under conditions where they shrink. The elongation ofthe fiber increases as is indicated in the patent. While the processesof U.S. Pat. Nos. 2,920,934 and 3,101,245 produce a fiber havingimproved dyeability, reduced tendency to shrink and reducedfibrillation, such fibers have the disadvantage of elongating underhot-wet conditions and are consequently undesirable for making fabricswhich are piece dyed, washed or steam pressed.

It is, therefore, an object of this invention to provide an improvedprocess for post treating extruded filaments prepared by spinning asolution of a polymer containing acrylonitrile. Another object of theinvention is to provide a process for improving the dimensionalstability of a fiber prepared from a polymer containing acrylonitrile bya wet-spinning process. Still another object of the invention is toprovide a method for making acrylonitrile fibers adapted to be used formaking fabrics which are to be exposed to hot-wet conditions such aswashing in water or steam pressing. A still further object of theinvention is to provide a fiber produced by spinning a solution of apolymer containing acrylonitrile which has good flexibility combinedwith improved dimensional stability under hotwet conditions.

The foregoing objects and others which will become ap parent from thefollowing description are accomplished in accordance with thisinvention, generally speaking, by providing a process wherein stretchoriented, relaxed and dried filaments are spun from a solution of apolymer containing at least about 95 percent acrylonitrile and aresubjected to wet steam under pressure but at a temperature below that atwhich the filament will shrink. It has been found that fibers spun froma solution of a polymer containing at least about 95 percent by weightacrylonitrile and heated with wet steam under pressure to a temperatureabove about 120 C. but below a temperature where they will shrink haveless tendency to elongate under hot-wet conditions than similar butuntreated fibers. Furthermore, the flexibility of the fiber is notdeleteriously affected by the steam treating step provided thecomposition of the polymer from which the fiber is spun contains atleast 95 percent acrylonitrile and the maximum temperature reached bythe fiber while subjected to steam is below the point where it willshrink while it is in a relaxed or tensionless state. The maximum steamtemperature permissible will vary from one polymer composition toanother depending upon the temperature where shrinkage begins. Forexample, an oriented, dried fiber having the composition of about partsacrylonitrile and 10 parts methyl methacrylate will shrink when heatedwith wet steam at 125 C. However, a fiber spun from a homopolymer ofacrylonitrile can be heated with steam up to about 160 C. withoutappreciable shrinkage while one spun from a copolymer of about 5 percentmethyl methacrylate and about percent acrylonitrile should not be heatedabove about 150 C. As a general rule for all polymer compositionscontemplated by the invention, the fiber is heated above about C. andthe preferred process contemplates heating the fiber with steam underpressure to a temperature of between about C. and C.

Generally speaking, in preparing the fiber having improved dimensionalstability under hot-wet conditions provided by this invention, ahomopolymer or copolymer containing at least about 95 percent by weightacrylonitrile is dissolved in a suitable solvent therefor, extruded intoan aqueous coagulating bath to form gel filaments, and the filaments arethen washed substantially free from solvent, oriented, dried, and heatedwith steam under pressure in the relaxed state while avoiding atemperature where the fibers will shrink to any appreciable extent.Stretching the gel filaments prior to washing and again after washing toorient the polymer molecules improves the strength of the fibers.Preferably, the filaments are stretched in air prior to washing freefrom solvent and are stretched again after washing and before drying.The second stretching process is preferably conducted in water at about80 C. or higher. Usually, the fibers are stretched to only two to fourtimes their unstretched length in air and are then stretched to 10 ormore times their original unstretched length in hot water. Surprisingly,it has been found that although no shrinkage or visible change occurs inthe fiber when it is heated with steam as provided herein, thedimensional stability under hot-wet conditions is improved as evidencedby a decrease in the tendency of the fiber to creep when exposed to hotwater. For some yet unexplainable reason, decrease in creep has not beenobtained when fibers spun from polymers containing less than about 95percent acrylonitrile are treated by the heat treatment process of thisinvention.

The stability of fibers under hot-wet conditions can be determined bysubjecting them to a creep test." The creep test is a standard test usedby the industry and differs from other static strength tests by takinginto account the element of time. In making such a test, the fibers tobe tested are mounted on clamps in the form of a loop from 5 to 10 cm.long. A load of 0.1 g. per denier of the fiber is suspended from thelower end of the loop. The loaded fiber is placed in water at 90 C. andthe length thereof is measured after 1 minute and again after 10 minutesin the water. The change in length or creep after 1 minute is known asE,. The change in length after 10 minutes exposure to the water is knownas E Delta creep is E minus E, or the change in length between the firstminute and 10th minute exposure.

The process provided by this invention reduces the tendency to creep offibers produced by spinning any polymer, copolymer, terpolymer or thelike containing at least about 95 percent by weight acrylonitrile so anyof the various wetspinning processes can be used to prepare the gelfilament. A preferred process is that disclosed by Cresswell in U.S.2,558,730 but any of the other wet-spinning processes known to the artcan be used, if desired. The fibers resulting from wet spinning, stretchorienting and washing may be dried by any suitable process including theone disclosed by Robertson et al. in US. Pat. No. 2,984,912. The fibersmay be relaxed prior to drying by shrinking with steam or they may berelaxed after drying. Relaxing or shrinking of the fibers impartsgreater flexibility thereto. Since very high temperatures are requir dto relax fibers having a composition of greater than 95 percentacrylonitrile after drying, it is more practical and preferred to relaxthem prior to drying. Temperatures of about 70 C. and higher are usedwhen relaxing or shrinking fibers before drying. The fibers should notbe stretched during treatment with steam as provided herein in order toavoid subsequent shrinkage under hot-wet conditions.

As indicated hereinbefore, the polymer from which the fibers areproduced may be a homopolymer of acrylonitrile or any other polymercontaining at least 95 percent by weight acrylonitrile and anothermonomer or two or more monomers which are polymerizable withacrylonitrile. Any suitable ethenoid monomer containing a CH C=groupwhich is polymerizable with acrylonitrile may be used and iscontemplated in an amount of up to about 5 percent by weight in thepolymer. Some specific examples of suitable monomers are methylmethacrylate, methyl acrylate, vinyl acetate and the like. Othersuitable monomers and polymers are disclosed in 1.1.8. Pat. No.2,883,260 and elsewhere in the art.

In preparing the solution to be extruded in making the fibers, thepolymer may be first dissolved in a suitable solvent to form a spin dopeor the polymer may be prepared by polymerizing monomer or monomers inthe solvent to be used in the spin dope. Any suitable water solublesolvent for the polymer may be used such as, for example, dimethylacetamide, dimethyl formamide, ethylene carbonate, the metalthiocyanates disclosed in Cresswell US. Pat. No. 2.588,?30 and the like.The filaments may be extruded into any suitable aqueous bath such as,for example, those disclosed in the aforesaid Cresswell patent.

In the following examples, all parts are by weight unless otherwiseindicated.

EXAMPLE 1 A spinning solution is prepared by dissolving about 11.2 partspolyacrylonitrile homopolymer, in about 88.8 parts of a 50 percentaqueous solution of sodium thiocyanate. The spinning solution isextruded through a spinnerette submerged in an aqueous coagulating bathcontaining about 14 percent sodium thiocyanate at a temperature of about0 C. The resulting filaments are removed from the coagulating bath,stretched in air to about twice their unstretched length and washed withwater at room temperature until substantially all solvent has beenremoved. The filaments are next stretched in water at about 98 C. toabout five times their washed length or, in other words, to about timestheir length prior to stretching in air. Skeins of the stretchedaqua-gel filaments are immersed in water at about 85 C. and allowed torelax for about 10 minutes at about 85 C. The skeins are removed afterthe water has cooled to room temperature (about C. The filaments relaxabout 19 percent of their fully stretched length. The skeins are nowconditioned in an oven having an atmosphere of about 127 C. dry bulb andabout 60 C. wet bulb and left until dry. The filaments relax anadditional 37 percent of their wet fully stretched length to a final drydenier of about 3.

A series of samples of fibers thus produced are treated in an autoclaveunder steam pressure for periods of 20 minutes at the temperaturesindicated in table 1. The results which are obtained in the creep testdescribed hereinbefore on the steam .treated samples and on an untreatedsample are recorded in Table l-(onlinucd Fibers are produced inaccordance with the process described in example 1 except a copolymcrhaving the composition of about 95.7 percent polyacrylonitrilc and about4.3 percent methyl acrylate is substituted for the homopolymer ofexample 1.

The extruded gel filaments are stretched in air to 2.5 times theirunstretched length. The filaments are then stretched in water at about98 C. to about 5.6 times their length after stretching in air or toabout 14 times their length prior to stretching in air. The denier isabout 1.9. Skeins of the filaments are gel-relaxed in water at about 98C. for about 10 minutes and shrink about 26 percent of their stretchedlength. The relaxed fibers are dried at about 127 C. dry bulbtemperature and about 60 C. wet bulb where they relax to a total of 37percent of the stretched length and a denier of about 2.8 per filament.

The filaments are steam treated as described in example 1 and measuredfor creep and elongation. The results are recorded in table 11.

'lAll LE 1 1 Percent Elongutlon lerccnt creep Shrink. 2... Steam tnmp.,C. ngo Strnlghl, Loop E1 E E r-E1 No treatment. 0 411. .1 211. .l 20.1120.11 1|. 1 120... 0 44.3 28.5 11.2 14.15 3.3 130. II 48. l 26. 7 l2. 7l5. 4 2. 7 H0. 0 40.11 29. 5 13. (l 10. 8 3. 8 150.. 3.0 43.5 30.7 15.821.3 6.5 100 H. 0 115. 2 61. ll 26. 4 0 311.0

EXAMPLE 3 The process of example 1 is repeated except the 10 minuterelaxation step in water is omitted. The dried fiber is heated withsteam to 127 C. The hot-wet creep is as follows:

TABLE 111 Fiber E, E A Dried only 26.2 30 3.8 Dried only 26.6 30 3.4Steamed at 127 C. 6.1 7.8 1.7

Steamed at 127 C. 8.1 9.1 1.0

It is to be noted that significant improvement in creep is obtained byheating the fiber with steam to a temperature where it does not shrinkeven when the gel relaxation step is omitted.

The term polymer of acrylonitrile" is used in the claims to mean anypolymer containing at least about percent by weight acrylonitrile andnot more than about 5 percent of one or more other ethenoid monomercontaining a CH C radical which is copolymerizable with acrylonitrile.

Although the invention has been described in detail for the purpose ofillustration, such detail is solely for that purpose and it is to beunderstood that variations can be made by those skilled in the artwithout departing from the spirit and scope of the invention except asit may be limited by the claims.

I claim:

l. A process for improving the dimensional stability of acrylonitrilepolymer fibers under hot-wet conditions which comprises (a) wet spinningan acrylonitrile polymer containing at least about 95 percent ofacrylonitrile by a .ocess which includes the steps of extruding,coagulating, stretching, washing, and drying the fibers so spun and (b)heating the thus dried fibers while in a substantially tensionless statein the presence of wet steam under pressure to a temperature above 100C. but below the temperature where substantial shrinkage of said fiberoccurs.

2. A process as defined in claim 1 wherein said acrylonitrile polymer isa homopolymer of acrylonitrile and wherein said fiber is heated tobetween 100 C. and about 160 C. with the steam.

3. A process as defined in claim 1 wherein said acrylonitrile polymercontains up to about 5 percent of another ethylenically unsaturatedcomonomer copolymerizable with acrylonitrile and wherein said fiber isheated to between l C. and about l50 C. with the steam.

4. A process as defined in claim 3 wherein said acrylonitrile polymercontains about 95 percent acrylonitrile and about 5 percent methylmethacrylate.

5. In a process for wet spinning acrylonitrile polymer fibers whichincludes the steps of extruding, coagulating, washing, stretching, anddrying the fibers so spun, the improvement comprising (a) using in saidwet-spinning process an acrylonitrile polymer containing at least aboutpercent of acrylonitrile and (b) heating such fibers subsequent todrying and while in a substantially tensionless state in the presence ofwet steam under pressure to a temperature above C. but below thetemperature where substantial shrinkage of said fibers occurs, therebyreducing the tendency of said fibers to creep under hot-wet conditions.

6. A process as defined in claim 5 wherein said acrylonitrile polymer isa homopolymer of acrylonitrile and wherein said fibers are heated tobetween 100 C. and about 160 C. with the steam.

7. A process as defined in claim 5 wherein said acrylonitrile polymercontains up to about 5 percent of another ethylenically unsaturatedcomonomer copolymerizable with acrylonitrile and wherein said fiber isheated to between 100 C. and about C. with the steam.

2. A process as defined in claim 1 wherein said acrylonitrile polymer isa homopolymer of acrylonitrile and wherein said fiber is heated tobetween 100* C. and about 160* C. with the steam.
 3. A process asdefined in claim 1 wherein said acrylonitrile polymer contains up toabout 5 percent of another ethylenically unsaturated comonomercopolymerizable with acrylonitrile and wherein said fiber is heated tobetween 100* C. and about 150* C. with the steam.
 4. A process asdefined in claim 3 wherein said acrylonitrile polymer contains about 95percent acrylonitrile and about 5 percent methyl methacrylate.
 5. In aprocess for wet spinning acrylonitrile polymer fibers which includes thesteps of extruding, coagulating, washing, stretching, and drying thefibers so spun, the improvement comprising (a) using in saidwet-spinning process an acrylonitrile polymer containing at least about95 percent of acrylonitrile and (b) heating such fibers subsequent todrying and while in a substantially tensionless state in the presence ofwet steam under pressure to a temperature above 100* C. but below thetemperature where substantial shrinkage of said fibers occurs, therebyreducing the tendency of said fibers to creep under hot-wet conditions.6. A process as defined in claim 5 wherein said acrylonitrile polymer isa homopolymer of acrylonitrile and wherein said fibers are heated tobetween 100* C. and about 160* C. with the steam.
 7. A process asdefined in claim 5 wherein said acrylonitrile polymer contains up toabout 5 percent of another ethylenically unsaturated comonomercopolymerizable with acrylonitrile and wherein said fiber is heated tobetween 100* C. and about 150* C. with the steam.